Systems are known in the prior art by virtue of which at least a part of a fixed artwork transparency is caused to give the appearance of motion in the image. This is typically accomplished by generating a broad beam of polarized light, the direction of polarization of which is systematically rotated, and passing this beam of light first through a polarizing layer transparent, or at least strongly translucent, polarizing elements which polarize light passing therethrough in respectively different transverse directions (hereinafter referred to as the polarmotion material, element or layer), and then through an artwork transparency; preferably, a light-diffusing layer is also provided between the polarmotion material and the artwork transparency. As is well known, these polarmotion elements transmit polarized light applied thereto to different degrees, depending upon whether the polarization axis of the material of a given element is parallel to that of the incident polarized light, in which case light transmission is a maximum, or is at right angles to the direction of polarization of the incident light, in which case the transmitted light is a minimum, or is at some intermediate angle in which case the transmitted light is at a corresponding intermediate level. Because of this arrangement, a beam of incident light having a rotating direction of polarization causes different ones of the polarmotion elements to become highly transmissive, i.e. brighter, at different times while others of the elements become successively less transmissive and in effect darker, to a degree depending upon the instantaneous angle of orientation of the incident polarized light. This changing of the brightness of different elements of the polarmotion material is typically used to produce progressive changes in the brightness of adjacent elements in the art transparency and a corresponding appearance of motion in the viewed image. In many cases, only portions of the artwork transparency are to give the appearance of motion, in which case only those portions are backed with polarmotion material.
The typical nature and theory of operation of such devices need not be set forth or explained herein in detail, since they are well known and are, for example, set forth in U.S. Pat. No. 3,054,204 of Donald N. Yates, filed Dec. 9, 1959 and issued Sept. 18, 1962.
While such apparatus has been successful for many purposes, it has been found that when the animated polarized light image is to be viewed not directly by the naked eye, but by means of optical systems which are sensitive to changes in the direction of polarization of light incident thereon, then undesired visual effects arise in the ultimately-formed image which is viewed by the eye directly.
A common situation in which these undesired effects occur, and with reference to which the invention will be specifically described hereinafter, is that in which an animated polarized light display is viewed by a color television camera of the usual type. A color television camera of the type employed in the U.S. system of color television typically includes beam splitters and/or dichroic mirrors or other optical devices which are sensitive to changes in the polarization angle of light incident thereon. Such a device will ordinarily reflect or transmit light with much greater intensity when the incident light is polarized along a specific direction than when it is polarized at right angles thereto, and with an intermediate strength for intermediate angles of incidence. Color motion picture cameras also typically employ similar optical elements having a similar sensitivity to direction of polarization of incident light.
More particularly, in such an arrangement the light reaching the camera or other optical device from any portions of the artwork transparency not backed by polarmotion material is polarized and has a rotating direction of polarization, the intensity of such rotating polarized light being however uniform as a function of time. Light reaching the camera or other optical device from the portions of the artwork transparency backed by polarmotion material is also polarized, but the light from any such image portion varies in time according to the instantaneous angle of orientation of the polarized light with which it is illuminated, and the light from different sets of similar polarmotion elements have respectively different directions of polarization.
When light from such a transparency reaches a dichroic mirror or other polarization-angle sensitive device in a viewing camera, such device acts similarly to a polarization analyzer in that it transmits or reflects an intensity of light which depends not only upon the intensity of the light incident thereon, but generally also upon the direction of polarization thereof, and also generally upon the angle at which the light reaches the dichroic mirror or similar device from the polarmotion transparency. Because of this, when viewed through the agency of a color television camera, portions of the viewed transparency which are not backed by polarmotion material will appear to "blink", changing from a very high intensity to a very low intensity twice for each rotation of the polarizing spinner.
As to those portions of the transparency backed by polarmotion material, although the light from each such portion remains at the same polarization angle, the intensity of light which it produces at any given time is distorted by the analyzing effect of the viewing camera. That is, if the polarization angle for which the camera is most sensitive is aligned with certain sets of elements in the polarmotion material, it will pass on such light without substantial diminution. However, light from those elements of the polarmotion material having polarization angles at 90.degree. to the effective polarization-analyzer angle of the camera will be passed on by the camera optics only to a very slight extent or substantially not at all. Light from the polarmotion material which is at intermediate polarization angles will be passed on by the camera optics to an intermediate degree. Furthermore, the angle at which the light reaches the camera optics, and hence the angular orientation of the camera with respect to the animated display, will also affect the extent to which the camera optics pass on the light incident thereon from the animated image. The result is that the carefully constructed animated polarized light image is greatly and unpredictably distorted by the camera optics, typically so that a smooth-flowing motion carefully built into the animated polarized light image by the fabricator becomes irregular, jumpy, and often loses all semblance of appearance of smooth flow under these conditions of viewing by typical camera optics which are sensitive to the angle of polarization of light incident thereon.
A specific and important aspect of the invention for commercial purposes lies in its use to produce video tapes of images at least part of which appear to possess motion. In the case of advertising materials, such as television station advertising of sponsor product or of its own services, programs or call letters, it is relatively cheap and convenient to make up a display of the desired type utilizing polarmotion elements and then to view it with a color television camera, the output of which is recorded on video tape. Such tape may then be utilized whenever desired during television broadcasting, in the usual way. Another important aspect lies in the production of video tapes for educational purposes, for example in explaining functions occurring in living things, or in explaining operations of machines or scientific devices. By creating such images first as images animated by polarized light and then converting them, by appropriate color television camera means, into color video tapes, a very simple and inexpensive method is provided for making such motion-containing materials available to the public.
Another aspect of the invention deals with the problems of image intensity and image definition. Color television cameras operate most successfully from very bright images and, as will become more apparent hereinafter, arrangements according to the present invention provide extremely bright images, such as cannot readily be obtained with projected or reflected images. Further, particularly in relation to educational displays, it is often desirable to enable the camera to concentrate upon and enlarge a relatively small section of the display to show it clearly in more detail, and unless the image presented to it is of relatively high definition, such detail will not appear as desired. The present invention also makes available such high difinition, as will also become more apparent from the discussion set forth hereinafter.
Accordingly, it is an object of the invention to provide new and improved apparatus for producing animated images by means of polarized light.
It is also an object to provide a new and improved lamination for producing animated images by means of polarized light (hereinafter referred to as the animating lamination).
Another object is to provide a new and improved system for obtaining color television images of animated displays produced by polarized light.
A further object is to provide the latter type of system with improved intensity and definition in the resultant color television image.
It is also an object to provide color television images from an animated display produced by polarized light, which images reproduce faithfully the original animated image without appreciable distortion from the appearance which the animated image would have when viewed directly by the human eye.
It is also an object of the invention to provide a new and improved system for producing color video tape of images at least parts of which have the appearance of motion.